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An enormous star, 150 times more massive than the Sun, has been discovered in the Large Magellanic Cloud, and it appears to be alone, with no other stars in its vicinity. This is very unusual, because very massive stars are normally found within very populous star clusters.
The star in question is called VFTS 682 (where VFTS is the acronym for an observing program at ESO, the VLT-FLAMES Tarantula Survey) and is located within the Tarantula nebula, the most active star forming region in the whole of the Local Group, the small collection of galaxies of which the Milky Way and the Andromeda galaxy are the main members.
VFTS 682 was already known to be a young star, very hot and very bright, but its mass had been underestimated due to the extinction of its light by dust in the surrounding nebula. This dust preferentially absorbs blue light, allowing more red and infrared photons to reach the observer, making the star seem redder than it really is, hiding the blue colour that characterises the most massive, hot stars.
The new interpretation of VFTS 682 comes from an international team of researchers led by Jorick Vink, Gotz Grafener and Joachim Bestenlehner, of the Armagh Observatory (Northern Ireland) who used the FLAMES spectrograph (multi-object, high and medium resolution) mounted on the unit 2 telescope (Kueyen) of the Very Large Telescope.
They determined a surface temperature of 50,000 K and a mass of 150 solar masses, making it one of the most luminous stars known.
It is still a mystery why it lies so isolated. It is very unlikely that it was born on its own (stars are thought to born in clusters) so an alternative explanation is needed. This may lie in the open cluster visible to the right of the above image, about 90 light years from VFTS 682 (indicated), at least as long as they are both at a similar distance from Earth.
The cluster is called RMC 136, and actually contains a star practically identical to VFTS 682, suggesting that the latter may have once belonged to the cluster, before being expelled via gravitational interactions.
This phenomenon should be rather common, but it is usually the smaller stars that get expelled after interactions with more massive bodies. An accurate determination of the proper motion of VFTS 682 would clearly help resolve the mystery around this extraordinary star.
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